Pneumatic hammer drills are known in which driving and percussion elements constituted by a motor-actuated drive piston and a freely moving percussion body, respectively, are accommodated in a rotating cylinder. The percussion body is caused to move back and forth with air acting as the coupling and buffer medium and further, the percussion body is controlled by means of a venting port disposed in the wall of the cylinder in the region of the pneumatic buffer. The rotating cylinder simultaneously serves to drive the tool holder which is fastened to the sleeve via an insert. Such an arrangement is disclosed in German Laid-Open Application (Auslegeschrift) No. 1,427,747. Due to the relative movement of the rotating cylinder with respect to the solely axially moving drive piston as well as with respect to the percussion body, there results, on the one hand, greater wear of the parts which move relative to one another and, on the other hand, sealing problems develop since sufficient play must be provided for rotation of the piston relative to the axially moving driving and percussion elements. Further the efficiency of the hammer drill is adversely affected by increased friction losses in the percussion mechanism. The consequence of reduced tightness between the inner wall of the cylinder and the parts of the drive piston and percussion body coming in contact therewith is that between two operating strokes the amount of air flowing through the venting port provided in the cylinder in the region of the buffer zone is no longer sufficient to make up for the leakage losses. Thus the striking effect of the hammer is reduced; furthermore, it may happen that the percussion body hits the drive piston. This is objectionable since it may damage, or even destroy the percussion system.